Hello.
Today I tried to access my old RB750, but I forgot password.
So I made a reset - everything worked fine, I got the default configuration.
Then I wanted to update router to current 6.39.1 (it was on 6.38)
After reboot i goot a boot loop - the device reconnects every few seconds.
So I tried to downgrade with netinstall, and I have a problem - it recognizes my router, but I cannot install the firmware - it shows "Sending offer for a second, then the progress bar is empty (like 0%), and then after 10-15 seconds router gets status “ready”, the install button can be pressed again, but the software isn’t installed.
I tried to install different versions of firmware, but with no luck.
Can you help me?
Are you trying to install the correct version of the software?
Did you try to do the configuration reset again?
There have been some issues with the latest version w.r.t. upgrading, especially when upgrading unconfigured routers.
OK - it works.
I used Netinstall from 6.38 and it worked.
Then upgrade from Winbox - and still working 
I upgrade RB750GL to routeros-mipsbe-6.42.4.npk. After the upgrade the router went into a Boot Loop.
I cannot do a factory default using the reset button.
I have tried to different Netinstall (netinstall-6.42.4 & netinstall-5.26) but I cannot connect to the router.
I am using Windows XP.
The network port is setup with.
IP: 192.168.88.2
MSK: 255.255.255.0
GW: 192.168.88.1
Network Booting set to 192.168.88.3 with the ethernet cable plugged into port 1.
The RB750GL never connects. It just keeps looping.
The LED1 comes on (showing a link) and blinks (showing the computer communication).
All 5 LEDs come on for about a 1/4 of a second then go out.
Then they come on again with the ACT LED.
I have tried powering it on with the Reset button depressed untill the ACT led blinks and then let go.
Then repeats.
It does not connect.
Use netinstall 6.40.8.
I finally figured out that you needed to hold down the reset button until after the ACT led stopped Flashing.
I was then able to download the firmware.
I tried to install three different RouterOS’s.
routeros-mipbe 4.17
routeros-mipbe 5.26
routeros-mipbe 6.42.4
After the install I rebooting the router. The first two would reboot and not go into a Boot Loop. The latest would consistently go into a Boot Loop again.
With versions 4.17 & 5.26 the router would not respond to Winbox in any of the 5 ports.
Just now I have brought the router back to our shop. I installed again the latest Routeros-mipbe 6.42.4.
This time I ran Winbox without rebooting the router after installing the Routeros with netinstall and I was then able to connect to the router.
I was also shown how to update the firmware System/Routerboard and did so.
I then rebooted the router and everything is OK.
Please make note:
-
When using Netinstall. After powering on the router holding down the Reset button. *** DO NOT RELEASE THE RESET BUTTON UNTILL THE ACT LED STOPS FLASHING ***
ACT led sequence (1) PWR & ACT leds come on solid. (2) ACT led starts flashing. (3) ACT led turns off. → release Reset button now. -
After installing the new RouterOS. *** DO NOT RESET, POWER OFF, OR REBOOT THE ROUTER *** Connect to the router using Winbox immediately!
Thank-you for your help.
I seem to be facing the same.problem on my RB750UP. Installed 6.42.6 through webfig, after restart the router seems to have gone to a bootloop sequence. Pwr+act+leds1-5 light up and then led 1 blinks rapidly for 1/4th a sec or so and it repeats.
Tried to use netinstall, held down the reset button till the act stops flashing. After that the router good through that bootloop sequence all over 
Netinstall only works when you read the directions carefully, and even then you need to get the feel of it.